In the first cohort, a total of 2506 saliva samples were collected and processed. The range of DNA yields and proportion of samples in each bin are shown in Table 2. 2255 samples (90.0%) met or exceeded the threshold of 20 ug total DNA. A further 150 (6.0%) samples with total DNA yield in the range 10–19.9 ug were reprecipitated. A total of 101 individuals (4%) whose samples yielded <10 ug were referred for resampling and 91 were successfully recontacted (with the remainder having separated from the University). Of 91 recontacts, 49 (53.8%) were resampled, and 40 (44.0%) gave total yields at or above the threshold value. DNA purity from this protocol is generally very good, with median OD260/OD280 ratios of 1.86; 75% of samples have an OD260/OD280 ratio ≥ 1.8 and 90% of samples have an OD260/OD280 ratio ≥ 1.7.
